Keying system



H. R. DYSON KEYING SYSTEM April 5, v1938.

Filed April 17, 1956 i Snventor Ha race R. Dyson attorney Patented Apr. 5, 1938 KEYING SYSTEM Horace R. Dyson, Oaklyn, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application April 17,

, Claims.

My invention broadly relates to keying systems. More specically my invention is a keying system for high power radio transmitters in which objectionable key clicks are substantially 5 eliminated.

The keying of a radio transmitter involves numerous diiiiculties. Among these are `the interference problems caused by key clicks and key thumps. Such interference is particularly objectionable when a number of transmitters are operatedV in close proximity to a number of receivers,-a condition often experienced on shipboard.

When keyed transmitters and receivers are being simultaneously operated in relatively close proximity, the key clicks have been found to set up transient currents in the receivers. These transient currents are caused by the abrupt building-up and sharp decay of a keyed transmitter wave. Numerous considerations make the elimination of key clicks highly desirable.

One of the objects of my invention is the elimination of key click or thump disturbances in a transmitted wave.

Another object is to so shape the envelope of the keyed transmitted energy that the interference caused by such keying is substantially eliminated by an inexpensive. and simply arranged apparatus.

A further object is to gradually build up the keyed wave and thereafter gradually reduce the keyed wave to eliminate the disturbing effects of abrupt keying. ,f

An additional object is to make the key cllck limiting device substantially independent of the transmitted frequency and practical for high keying speeds.

My invention may be best understood by referring to the accompanying drawing in which Fig. 1 is a schematic diagram of one embodiment of my invention, and

Fig. 2 (A, B, C) are illustrations of a conventionally keyed carrier wave, a carrier wave keyed in accordance with my invention, and relative 45- keying characteristics of the several stages of a transmitter keyed in accordance with this in- Vention.

Referring to Fig. 1, a suitable key I is connected by relay means 2 to two pairs of relay key contacts 3, 5. The relay is arranged so that one pair of the key contacts 3 close slightly before the other pair of contacts 5. This allows the master oscillator and driver stages 1 to energize the power amplier grid 9. However, the screen grid Il of the power amplifier I2 is ini- 1936, serial No. '14,852

tially biased negatively to cut 01T the anode current of the power tube, and the power tube will therefore not be. instantaneously energized.

Shortlyafter the iirst pair 3 of key contactsl are closed the second pair 5 of relay key contacts 5- closes by means of a suitable mechanical connection between the pairs of contacts. This short circuits the biasing resistor I3 and allows the capacitor I5 to discharge through the resistor I1. Before the closing of the second pair 10 5 of key contacts, the grid electrode I9 of thermionic tube 2| was suciently negatively biased by the potential across resistor I3 tocut-ofl the current tending to flow from the cathode 23 -to the anode 25.

The gradual discharge of the capacitor I5 through the resistor I1 gradually decreases the negative bias on the grid I9, thereby permitting gradual building up of current through the cathode, anode and anode circuit resistor 21. The current flowing through the anode resistor 21 establishes a voltagedrop across this resistor. This voltage minus the voltage dropacross the bias resistor 29 will be applied to thescreen grid II of the power amplifier tube I2. Thus, the screen grid II which was initially negative with respect to ground becomes positive and thereby permits anode current to flow ,in Vthe power amplifier tube, which now assumes its normal load.

The anode current flowing through the cathode resistor 30l to ground produces a voltage drop across the cathode resistor which positively biases the vacuum tube 3|. The anode battery 33 is chosen so that substantially no current flows in the field winding of the latching relay 35 when the grid 31 is at zero voltage with respect to the cathode 39. When the grid 31 becomes positive with respect to cathode 39, current owing in the eld winding of the relay closes the relay contacts 4I which are in parallel with the relay key contacts 3. Since the plate or anode current from the power ampliiier I2 varies during keying, it is essential that the latching relay contacts remain closed until the anode current of the power amplifier practically ceases.

When the key I is opened and the keying relay is deenergized, i. e. during start of a space, the latching relay 35 contacts 4I, in parallel with the relay key contacts 3, remain closed until the power amplifier current nearly ceases. During this last mentioned interval the second pair of relay key contacts 5'open which allows bias voltage to gradually build up across capacitor I5 through resistor I1. The gradually increasing bias slowly cuts oif the anode current in tube 2I. Thus, the current through resistor 21, and the shunting capacitor 28, is slowly reduced to zero.

Since the bias voltage on the screen grid II depends upon the difference in voltage across the anode resistor 21 and across the resistor 29, it will be apparent that with zero voltage across the bias resistor 21, the bias voltage on the screen grid I I will be that across resistor 21` and will be negative with respect to its cathode 8. With the screen grid II negatively biased, the anode current in tube I2 will become zero, the bias voltage between the grid 31 and the cathode 39 of'tube 3I will be zero, the latching relay will. therefore open, and the master oscillator and' driver stages thus de-energized.

Thus, I have described how the master oscillator and driver stages of a transmitter may be abruptly keyed and substantially no disturbance. y

ofj a4 signall or carrier current keyed: in accord-- ance'with my invention. Fig. 2C'y is a graph representing the relative keying, with respect to time, ofthe master oscillator andi driver, andin power amplifier stages.

The actual tube equipment, voltages, resistor and capacitor valueswill be determined by the type and power of thev transmitter to be keyed. If a sensitive relayv of the proper characteristics is employed, the vacuum tube 31| may obviously be omitted and: the relay connected directlyY across theA biasing resistor, or in series therewith. The manufacturers normar ratings off the several parts may be' followed. By way of example, one suitable'set of tubes, constants and voltages have been indicated onV theaccompanying drawing.

I claim as my invention:

l. A keying system for a source ofi oscillationsY and a power ampliiierl connected tolsaid source, comprising means for keying said source, a pair ofthermionic tubes connected'to said power' amplifier, means connected to said pair of tubes for" biasing each of said tubes to. cut-off during spacing intervals, means connected, to said vpower' amplier and tothe iirst of.' said pair of tubes for biasing, said power amplifier to. cut-01T` during spacing signals, means including'the rst of said; pair of tubes for overcoming the cut-ofi bias of' said power ampliiier, means including saidpower amplifier for reducing the cut-off' bias of the second. of said. tubes, meansV including said second' tube for temporarily continuing the key-l ing of said source, and keying means connected to said source and to the rst of said pair of tubeswhereby a marking signalrst keys said source, then removes the bias on the first of said pair of tubes thereby permitting anode currents to iiow, which currents remove the cut-oil bias on said power amplifier, thereby biasing the second of said pair of tubes to maintain the keying of said oscillator, and further arranged to restore the aforesaid cut-off biases during spacing before de-energizing said source, of oscillation.

2 A keying system for a source, of oscillations and a power amplifier connected to said source,

comprising means for keying connected to said source and to the first oi' said pair of tubes, a painofv thermionic tubes, the iirst of said tubes haring its output circuit connected to said power amplier, and thesecond of said tubes having its input circuit connected to said power amplifier, means connected to said pair of tubes and to said power amplifier for biasing each of said tubes to cut-olf during spacing intervals, means including said power amplifier for reducing the cut1-`oif:lfias` of the secondoi` said tubes; means including said secondv tube for temporarily continuing the keying: of said' source, means con-- wherebyI said keying means is so constructed and arranged' that a marking signal first keys said source, then removes the bias on the rst of said pair of tubes thereby permitting anode currents to flow, whichcurrents remove the cut-01T biasV on said power amplifier, thereby biasing the secondi of' said. pair: of tubes to maintain the keyingof said oscillator, and further arranged to restore theaforesaid cut-oir biases during spacingv before: de-energizing said' source of oscillations'.

3. A deviceV of the character of claim l further characterized by the inclusion of means for gradually energizing and gradually de-'energizing'said power ampliiier.

4; A keying system for a source of oscillatory currents and a power amplifier, including a screengrid', connected thereto` which comprises a thermionic tube, meansl for biasing said tube during-- spacingA signals to substantially cut-off, meansl for'Y biasing saidl screen grid to de-energize said power amplifier,` a connection from said tube to said screen grid biasingl means wherebyY anode currents in saidv tube oppose the screen bias-means, means for keying said source, meansk for removing the bias on said tube and thereby positively' biasing said screen. grid after sai-d source is keyed, and means including saidpower amplifier for continuing the energizationV of said source until a spacingV signal substantially deenergizes saidpower amplifier.

5. AdeviceY of the character of claim 4 includiov.

, 601 ing means for gradually removing the bias on said screen grid during marking signals and gradually restoring said bias duringspacing signals.

HORACE R. DYSON'. 

